Field of the Invention
This invention relates generally to gas discharge light sources.
Description of the Related Art
Volatile organic compounds and other organic chemicals are widely used as solvents, degreasers, coolants, gasoline additives, and raw materials for other synthetic organic chemicals. These organic compounds are commonly found as trace contaminants in municipal and natural water streams. As a group, they are referred to as total oxidizable carbons (TOC). These compounds are very difficult to remove by conventional means, such as filtration and absorption by media such as activated carbon.
Exposure to ultraviolet light (UV) is a means of removing TOC from water in ultra-pure water systems. The ultraviolet light for TOC removal in current commercially available systems is produced by low-pressure mercury vapor lamps operating at the 185 nm wavelength. There also exist systems using pulsed light sources that produce broad spectrum light below 250 nm. These pulsed light sources are typically xenon flashlamps. Excited dimer (“excimer”) pulsed discharge lamps have also been proposed for removing TOC. Continuous discharge excimer light sources have also been proposed. Examples of these devices are disclosed in U.S. Pat. No. 7,439,663 to Cooper et al., which is incorporated herein by reference.
Excimer light sources to date use noble gas excimers (e.g., Xe2*, Kr2*, etc.) almost exclusively. The wavelengths of light which can be generated by noble gas excimers is limited, and noble gas-halogen excimers (e.g., ArF, KrCl, etc.) can generate light at some very useful wavelengths not achievable with noble gas excimers. The reason that noble gas-halogen excimers are only used in a very few applications is due in part to the fact that the halogen gases (e.g., F2, Cl2) that are used to form these excimers are highly reactive and chemically attack most materials used in these devices. This impedes the operation of the light source and ultimately damages it beyond repair, usually before a practical operating life time is achieved.